The overall goal of this Exploratory Development Research Grant is to investigate whether bacterial infections suppress lymphatic function and thus inhibit immune response. This will lend initial insight into new ways to manage difficult-to-resolve infections, many of which currently require intravenous antibiotic treatment that can lead to antibiotic resistant bacteria strains-another significant problem. The PI is an expert in lymphatic research, especially functional studies using novel intravital imaging technologies and animal models. He has assembled a first class team consisting of Dr. Dai Fukumura, an expert in nitric oxide biology, Dr. Nancy H. Ruddle, an expert in immunobiology, cytokines and autoimmune diseases and Dr. Jean C. Lee, an expert in s. aureus biology and vaccine development. This robust and experienced research team, along with the resources available in the Edwin L. Steele Laboratories, Massachusetts General Hospital and Harvard Medical School, ensure an optimal environment for the innovative studies proposed in this EDRG. Initial lymphatic vessels take up interstitial fluid to create lymph that is transported through collecting lymphatic vessels and lymph nodes, and eventually returned to blood circulation to maintain tissue fluid balance. Antigen and antigen presenting cells (APC) use this route to enter the draining lymph node (LN) and initiate an immune response. Chronic infections, such as in cellulitis, are frequently associated with lymphedema, which is generally associated with malfunctions or disruptions in the function of collecting lymphatic vessels. Cases of cellulitis are responsible for nearly 400,000 hospital admission each year in the US. In this Exploratory Developmental Research Grant proposal we will test the hypothesis that these difficult-to-resolve infections are aided by an impairment of autonomous contraction of lymphatic vessels draining the infected area, thus limiting signaling to the lymph node and causing toxin accumulation at the site of infection. We will use our novel murine model that allows autonomous lymphatic contractions to be imaged and quantified intravitally. We will study the impairment of lymphatic function during s. aureus infection (Aim 1), the role of host derived nitric oxide from myeloid derived suppressor cells in causing lymphatic impairment (Aim 2) and the role of nitric oxide produced by the s. aureus nitric oxide synthase on lymphatic function (Aim 3). To achieve these Aims we will measure the strength of lymphatic contraction, lymphatic flow, antigen transport and duration of infection. We will characterize the biological response to the experimental conditions using standard cell biology, biochemistry and molecular biology techniques. These aims will enable us to address whether blocking nitric oxide is a therapeutic option to enhance the clearance of bacteria during s. aureus cellulitis. This EDRG proposal lies at the crossroads between immunology and functional lymphatic biology, an intersection that has been understudied to date. The work proposed here will drive this field by applying the principals of lymphatic function to study the important public health problem of s. aureus skin infections.